Efficacy of Friction Stir Welded Joints Under Fatigue Loading: A Critical Review

Abstract

The current research primarily reviews the efficacy of FSW joints under fatigue loading conditions. The review starts with elaborating the working principle of FSW process along with its advantages and applications in the industry. The impact of the FSW process on the mechanical properties of the materials being joined is discussed. The possible enhancement of mechanical properties by particles inclusion during FSW is also elaborated. It is observed from literature that the inclusion of copper nano particles, Al₂O₃ particles and SiC microparticles proved to be effective in improving the mechanical properties of FSW joints.

The performance of FSW joints under fatigue loading is reviewed in detail. Several researchers investigated the influence of process variables on the fatigue performance of different materials joined using FSW. High-quality FSW steel joints surpassed high-quality arc welds, with fatigue strength increasing with material yield strength. It is observed from literature that fatigue response of FSW joints not only depends on the process parameters but also on external factors like stress ratio, residual stress, defects, weld orientation side etc. It is also worth noting that, inducing compressive stresses in the FSW joints can increase their fatigue life. Post-weld treatments can decrease fatigue crack growth rate and enhance material fatigue life in FSW joints. Laser peening was observed to be effective in reducing growth rates of fatigue cracks and improving the overall fatigue life of FSW joints. FSW joints exhibited a fatigue strength approximately 20% higher than the GMAW joints, and at high stress amplitudes, the FSW joints had a lifespan about three times higher than that of the GMAW joints. There appears to be an opportunity to improve the fatigue response of FSW joints further by suitable nano-particles inclusion during the welding process.

The current review enabled the researchers to identify a research gap in the area of notch fatigue analysis of FSW joints. This needs to be explored further by creating notches of different geometries on the FSW joints and quantifying the impact of notch geometry (depth, width, perimeter length etc. of notch) on their fatigue performance. It is also observed that, literature in the area of evaluating the fatigue performance of FSW joints at different temperatures is scarce. This area can also be further explored.